According to a known method related to an eyelid detection using a face image, a state of the eyes in the face image is determined, and a direction of a visual line of a human is measured on the basis of the state of the eyes, or an awakened level of a human, for example, a driver's awakened level, is estimated on the basis of an opening level of the driver's eyelids. In this method, the eyes need to be accurately detected in the face image in order to determine their state, and the eyelids need to be accurately detected in order to detect the opening level of the eyelids.
For example, according to a device disclosed in JP03202045, a driver's state is determined by detecting an iris portion in a face image. Specifically, an area in which the iris portion is searched is firstly set in the face image, and in this searching area, a size of the area in which a color is relatively dark is calculated, and a central position of the iris portion is detected by weighing possible central points of the iris portion through a statistical procedure depending on the size of the dark area.
Generally, when a human is shown in a picture, eyes of the human may appear red as a result of a red-eye effect. The red-eye effect generally occurs as follows. When the human is positioned in a poorly lighted environment, light enters through his/her pupils, which are wide opened in the poorly lighted environment. The light reflects on choroideas of the eyes and exits through the pupils, and then the camera captures this reflected light which has now passed twice tough the pupils. When the human is illuminated with a flash, the light of the flash passes too fast for the irises of his/her eyes to close the pupils, as a result, the red-eye effect occurs in the picture. When a subject is illuminated with the flash for a certain moment, because the pupils are is diminished in size during that moment, the red-eye effect may not occur.
Further, when the driver's face is captured by the camera in the poorly lighted environment and when illuminated by means of the flash, because the flash illuminates with visible light the flash may disturb the driver. As another option, the driver's face may be illuminated with a near-infrared light. However, when the near-infrared light passes through the pupils of the driver, because the pupils are not diminished in size, the red-eye effect occurs continuously.
According to the known art, in the face image where the red-eye effect occurs, because the pupils are determined as a bright area, an iris of the eye, which usually exists in a dark area in the image, may not be appropriately detected. Further, when the pupils are detected in the image where the red-eye effect occurs, an edge of the pupils may be mistakenly detected as an edge of the eyelids.
A need exists for an eyelid detecting apparatus, an eyelid detecting method and a program thereof which is not susceptible to the drawback mentioned above.